Truss constructions



Jan. 13, 1959 c Tos 2,868,146

TRUSS CONSTRUCTIONS Filed Aug. 6, 1952 5 Sheets-Sheet 1 INVENTOR ATTORNEYS Jan. 13, 1959 C. MACKINTOSH TRUSS CONSTRUCTIONS 3 Sheets-Sheet 2 Filed Aug. 6, 1952 INVENTOR ATTORNEYS Jan. 13, 1959 c. MACKINTOSH 2,868,146

TRUSS CONSTRUCTIONS 3 Sheets-Sheet 3 Filed Aug. 6, 1952 INVENTOR ATTORNEYS United States Patent TRUSS CONSTRUCTIONS Charles. Mackintosh, Los Angeles, Calif.

Application August 6, 1952, Serial No. 302,905

1 Claim. (Cl. 108-23) This ,invention relates to wooden truss constructions of the general type used to support roofs of building structures of various kinds, and more particularly to certain joints or connections between elements of both the upper chord, the lower chord, and the web of the truss.

The g neral object of the invention is the provision of novel and improved wooden truss. constructions, as distinguished from, trusses fabricated from metal; the wooden trusses provided by the present invention being more practical, more economical, stronger, and more easily shipped and assembled than the truss constructions heretofore available.

The novel construction is more practical because the I difficulty of making accurately fitting deep joints in the timber at the junction of abutting elements is reduced; more economical in that elements of smaller size may be used; stronger since the forces are carried in such manner as to give a greater degree of rigidity to the upper chord compression elements; more easilyshipped because the novel construction permits greater lengths between panel points and consequently fewer individual members for each truss; and more easily assembled both because of the fewer members and because of the fact that the nature of the connectionsis such ,as to obtain maximum values from them, whereby they are smaller than in the conventional truss and the simplest materials are used in providing them, no special connectors being required but only standard bolts and small readily obtainable plates and angles.

In its preferred embodiments, the invention contemplates the provision of metal plates between the ends, of the upper chord elements where they would normally abut each other, the metal plates, however, being of such size that they occupy only the lower portions of the space between the members. One serious disadvantage in the construction of timber trusses in which the elements, of the upper chords abut each other end to end, is that it is very difficult to prefabricate the members of, the truss, or even to lay out the truss on the jobwith cuts of, such accuracy that the ends of the abutting members actually contact each other for the full height of the cut. Usually the cut at the junction of the abutting elements is open either at the top or at the bottom; thus, the location of the thrust between the members maybe at the top or at the bottom of the joint, thisuncertainty and possible nonuniformity rendering the structure much weaker than it should be for the material used and giving rise to a condition where the engineer cannot design a satisfactory truss without waste of material. Also, since the straight timber elements in a truss of this character generally carry considerable loads as beams, they are subjected to considerable bending stress and are therefore larger than, would be required for sustaining thrust stresses alone, and consequently have larger end areas than are required for taking care of the thrust between adjacent members of, the chord. Theadditionofthe short bearing plate in the lower part of'the joint offers a unique solu-' Patented Jan. 13, 1959 members at a known point which renders the engineering and designing of the truss more certain and makes any inaccuracy in the carpenters execution of the joints of far less importance, and also permits sufficiently accurate prefabrication.

Additionally, the novel short bearing plate, being lo- .cated in the lower half of the joint, greatly reduces both the bending stresses and the bending deflection of the upper chord members abutting said plate, by providing a negative moment at these ends of the upper chord members, which moment is opposite to the downward moment of the bending caused by vertical loads, such as the roof loads, thereon. For example, if the negative moment introduced by the short bearing plate is made equal to one-half of the bending moment caused by vertical loads, the maximum resulting bending moment in the timber upper chord is only 50% of that which would exist under the usual methods of construction. It is true that it would be 50% positive in the middle of the upper chord segment and 50% negative at its end, but this may be considered an ideal situation inasmuch as the timber beam is equally adequate for both positive and negative moments. Thus the timber is used far more efficiently, and in this example also the deflection of the timber due to beam action is reduced by about An additional feature which characterizes the invention is the metal connecting device which serves to join the upper chord segments or elements of the web members at their points of intersection, and transfer the loads between said segments and members in the simplest and most direct fashion, by making a maximum use of the bolts employed and, in the preferred form, providing lateral stability across the joint for purposes of facilitating the erection and bracing of the truss. In the past, large unitary metal plates have been used to connect the timber members at such intersections, but these are expensive and wasteful of material, and do not provide the desired lateral stability such as is required to hold the upper chord in line, for example, when the truss is pulled up to a vertical position from the horizontal position where it is assembled on the ground. In the practical execution of' the invention, use is made of an angle plate and one or more metal straps welded to it. This provides a combination in which stock materials only are employed and in which a minimum of material is used in providing lateral stability across the joint. Furthermore, the bolts used in the connection are each stressed only in end grain direction on the wood, thus ensuring maximum strength.

Another feature of the invention concerns the provision of a similar short bearing plate between the ends of the terminal segments of the upper chord and the heel strap which forms a part of the heel shoe bearing structure at the ends of the truss where the upper and lower chords join.

Finally, the combination of the features of providing the short bearing plates between the upper chord segments, the metal connecting devices at the joints, the heel shoe bearingupon the lower portion. of the endsegment of the upper chord rather than on the full end portion thereof, together with a unique lower chord splice, andthe provision of an upper chord wherein the thrust points at the ends of each segment thereof lie upon the arc of. a parabola or as near thereto as architectural requirements will permit, results in a structure of maximum effectiveness whereby all stresses are carried in the most direct manner possible within the limitations of the materials under consideration. This will be clearly understood from the following considerations.

Whereas formerly most timber truss manufacturers have had to resort to various bow-string or curved upper chord truss elements which are either bent or bandsawed to shape, the present invention provides means for utilizing straight segments available in any lumber yard where the timber can be used to its fullest extent by means of the novel short bearing plates. The metal connecting device, by imparting lateral stiffness, makes the overlapping of the upper chord members, such as is common in bow-string trusses, quite unnecessary. The present novel connection has also made it possible for the web members to be concentric and to carry their stresses in the most direct manner, whereas in the past most truss manufacturers found it only economical to use weaker eccentric connections. The lower chord stresses are carried in the most direct manner from end to end of the truss with the end shoes providing the negative moment in the outer segments of the upper chord to correspond with the negative moment provided at the ends of all other segments of the upper chord. By placing the thrust points of the upper chord more accurately upon a parabolic curve, the amount of stress in the web members on a uniform vertical load is reduced to zero since the moment under a uniform vertical load when plotted graphically is a parabola.

Other objects and features of novelty will be apparent from the following specification when read in connection with the accompanying drawings in which certain embodiments of the invention are illustrated by way of example.

In the drawings:

Figure 1 is a somewhat diagrammatic view in front elevation of the left-hand half of a symmetrical parabolic bow-string truss construction embodying the principles of the invention;

Figure 2 is a fragmentary view on an enlarged scale in a front elevation of the apex portion of the truss shown in Figure 1;

Figure 3 is a vertical transverse sectional view taken on line 33 of Figure 2;

Figure 4 is a fragmentary view in horizontal section through the heel portion of the truss and taken on line 44 of Figure 1;

Figure 5 is a front elevational view of another and simpler form of truss according to the invention;

Figure 6 is a view in front elevation of the right-hand half of a symmertical truss of the bow-string type being longer and having more compression elements in the upper chord than the truss shown in Figure 1;

Figure 7 is a fragmentary elevational View on an en larged scale of the heel portion of the truss shown in Figure 6;

Figure 8 is an end view of the heel portion of the truss;

Figure 9 is a view in horizontal section of the heel portion taken on line 9-9 of Figure 6;

Figure 10 is a fragmentary diagrammatic view in elevation of the framework of a building showing a nonparabolic tandem truss construction embodying some of the features of the invention, but designed for supporting a relatively flat roof for drainage of large roof areas;

Figure 11 is a fragmentary view on an enlarged scale of a portion of one of the truss spans of Figure 10;

Figure 12 is a fragmentary view on a further enlarged scale of a joint between two upper chord members of the truss shown in Figure 11 and certain of the supplemental roof supporting structure; and

Figure 13 is a fragmentary view in horizontal section taken on line 13-13 of Figure 11.

The truss construction designated generally by the reference numeral 10 in Figures l-4 of the drawings is gencrally of the parabolic bow-string type and designed for relatively short or medium spans. The upper chord of the truss 10 is composed of four compression elements or members abutting end to end, two of the members typitied by the one shown at 12 terminating in the heel portions of the truss and the other two members 14 and 15 abutting at the central portion of the truss to form the apex thereof.

The lower chord of the truss is made up of two end elements 16 (one of which is shown in the half view in Figure 1) and a central element 17 which is spliced to the end element 16 by a novel joint connection which will be described presently. The upper and lower chords are connected at intermediate points by the centrally disposed web elements 18 and 19 and the end web elements typified by the left-hand one shown at 20 in Figure 1. The connection of the abutting ends of the upper chord segments 14, 15 at the apex of the truss is shown most clearly in Figure 2 of the drawings. A preferably rectangular metal plate or shim is inserted between the otherwise abutting faces 26 and 27 of the ends of the respective elements 14 and 15. It will be noted that the plate 25 is of relatively small area as compared with the entire areas of abutment faces 26 and 27 and thus effectively reduces the calculated points of transfer of stresses from one of the chord segments to the other. This not only concentrates the thrust but eliminates the results of inaccuracies in sawing or cutting the ends of the elements 14 and 15 whereby if the surfaces 26 and 27 were in actual abutment, the point of stress transfer would vary from the top to the bottom of the truss.

In either erecting the truss on the job, or prefabricatmg it, the ends of'the segments or elements 14 and 15 of the top chord are connected by means of the angle pieces 30, one flange 31 of which is bolted to the sides of the end portions of the respective segments 14 and 15 as by means of the bolts 32 and the horizontal flange 33 extends outwardly and lends rigidity to the connecting plate. As shown in Figure 3 of the drawings, this form of connection may be employed upon both sides of the joint which is the desirable construction in most cases.

The abutment plate or shim 25 may be secured in place in any suitable Way, but two conjoint or alternative means are shown in the single Figure 3 of the drawings. For example, the plate may be secured to one of the elements 14 or 15 by means of the nails 34 passing through openings therein and driven into the end surfaces 26 or 27 or the plate may be marginally welded to the angle plates as suggested at 35.

For the purpose of making a strong unitary or integral joint, embracing the web elements as well as the segments of the upper chord, the narrow strips or plates 38 and 39 are welded as at 40 to the lower edge of the angle piece 30 at such angles as to correspond to the angularity of the web elements 18 and 19. The plates are bolted to the respective web elements by means of the bolts 42.

A similar connection is effected between the abutting ends of the elements 12 and the respective elements 14 and 15, wherein a similar abutment plate is interposed between the adjacent ends of the abutting segments and the segments are connected by means of the angle plate 47 to which is welded or otherwise secured the plate or strap 48 which is bolted to the upper end of the web strut 20 which extends from this joint to the lower chord of the truss. Of course, the joint structure 47, 48 may be repeated upon the opposite face of the truss at the two points of abutment described.

Another novel feature of invention resides in the provision of a unitary connecting plate which serves both to splice the lower chord elements and to connect the lower ends of the web members thereto. One of these connections is shown in Figure 1 of the drawings at 50 and of course may be repeated at the opposite side of the truss. Three narrow plates or straps are welded together at angles to correspond with the angles of the elements 17, 18 and 20 and are respectively secured thereto, the rather elongated plate 52 being bolted to the element 17 as by means of the bolts 53, the plate 55 being bolted as at 56 to the lower end of the Web strut 18, and the plate 58 being bolted as at 59 to the lower end of the. web strut 20. The plate 52 is elongated so that it overlaps the end of the lower chord element 16 which abuts the element 17 and is secured thereto as by means of the bolts 60.

The heel connection of the truss comprising this embodiment of the invention is shown at the left-hand end of Figure 1 and in the sectional view comprising Figure 4. .The extreme end of the lower chord element 16 is bevelled off to correspond to the angularity of the lower edge of the end element 12 of the upper chord and the end of this latter element is also bevelled off to conform to the horizontal plane of the lower edge of the element 16. The end 63 of the upper chord member 12 is preferably cut vertically and surrounded by the U-shaped strap 65, the bight 66 of which embraces the end 63 and is separated; therefrom by means of the small plate or shim 68 which extends only for a short distance up the height of the end face 63. The side arms of the strap 65 are bolted at 69 adjacent the bight portion to the end of the upper chord element 12 and are both bolted as at 70 near their outer ends to the lower chord element 16. A large diagonal bolt 72 may be inserted through openings in the respective elements 12 and 16. It will be noted that the strap 65 and the shim plate 68 provide a substantially localized bearing or thrust point at the ends of the parabolic upper chord of the truss.

The same principles may be applied to a triangular truss of extremely simple construction such as shown in Figure 5, although certain properties of the parabolic truss will not be present. In this embodiment the truss is designated generally by the reference character 75 and comprises the upper chord elements 76 and 77 which are joined by the single lower chord element 78. A central vertical strut 79 provides the web element. The abutting bevelled ends of the chord elements 76 and 77 are connected by means of the angle piece 80 which is provided with the rigid extension 81 secured to the upper end of the web piece 79. The abutting ends of the elements 76 and 77 are furnished with the abutment plate 82, this joint corresponding in general with the one shown in Figure 2 of the drawings, with the exception that there is but one web post to be considered. The foot of the centrally disposed web post 79 rests upon the mid-portion of the lower chord member 78 and is secured thereto by means of a T-shaped plate 85 consisting'of the vertical arm 86 bolted to the post 79 as at 87 and the cross-piece 88 bolted at 89 to the chord 78. At the ends or heel portions of the strut the connection is practically the same as shown in Figure 1 of thedrawings, the end portions. of the upper chord elements 76 and 77 and of the lower chord element 78 being bevelled to fit and connected by means of the U-shaped strap member 90 which is bolted to the chord elements and embraces the ends of the upper chord, elements' 76 and 77 with the small abutment plate 92 interposed therebetween.

In the embodiment illustrated in Figures 6-9 inclusive there is illustrated a longer and somewhat more elaborate truss structure, the upper chord of which comprises the elements or segments 100, 101, 102, 103 and the counterparts of elements 100 and 101 upon the left-hand side of the truss, which are not illustrated in the fragmentary view in the drawings. The lower chord is composed of the central tension element 105 and the end elements 106, only one of the latter elements being shown in Figure 6. The elements 105 and 106 abut at 108 and are secured together by the cheek plates 109 which are securely fastened to the ends of the elements 105 by means of the bolts 110. The abutting faces of the comparison elements 100-103 inclusive are separated by means of the small abutment plates 112 which are similar in all respects to the plates 25 and 82 of the previously described embodiments. Also, the angle plate assemblies 115 and 116 are put together and applied in exactly the same way as the plate assemblies 30, 38, 39 shown in Figures 1 and 2 of the drawings; and the angle connector plate assembly 118 between the compression elements and 101 is in all practical respects the same as the assembly 47, 48 of Figure 1, or assembly 80, 81 of Figure 5, and these elements therefore need not be described in any detail.

Web elements 120, 121, 122, 123, 124, etc. are provided and connected into the upper chord joints in the manner already described and they are connected to the lower chord elements an 106 by means of the strips or plates and 131, the upper ends of these plates being bolted as at 132 to the lower ends of the web pieces and connected to the lower chord members and to each other by the bolts 135.

The ends of this truss are shown as resting upon the posts or columns and the heel constructions of the truss will now be described with particular reference to the enlarged views of Figures 7, 8 and 9. The ends of the lower chord elements 106 are bevelled off diagonally to fit against the lower edge of the upper chord member 100 along the surface 142. An abutment plate is applied to the end surface of the upper chord member 100 and two U-shaped strap elements 146 and 147 surround the ends of the chord elements and are bolted to the element 106 by means of the bolts 149 and 150, and the upper member 146 is also bolted as at 152 to the upper chord element 100. U-shaped bight portions 155 and 156 are formed respectively in the strap members 146, 147 and are spaced outwardly from the abutment plate 145. Between the plate 145 and the bight portions of the straps which surround the whole assembly there is interposed a mass of dry-pack mortar indicated at 160. The abutment plate 145 may be tack welded as at 161 to the side portions of the straps 146 and 147 in order to position it properly within the joint. Angle irons 164 and 165 may be bolted to the bight portion of the lower strap member 147 as at 166 and secured to the top of the post or column 140 as by means of the bolts 167.

in Figure 10'- there is illustrated in a very diagrammatic way a. building framework comprising tandem trusses for supporting a fiat roof, the individual truss unitsbeing indicated at 175, 176 and 177, these units resting upon the columns 178, 179 and 180. In order to show the details of the connections, a fragmentary portion comprising a little more than one-half of the truss unit or panel 175, indicated by the bracket 182 in Figure 10; is shown; in Figure 11 of the drawings. These trusses are not of the parabolic type, but the upper chord iscomposed of inclined upper end elements 185 and at least two substantially horizontal intermediate elements 186 and 187. Sub-structure for carrying the horizontal: root" between the tandem trusses is shown at 190 and 191 in the diagrammatic view comprising Figure 10.

The lower chord of the truss panel 175 selected for illustration in Figure 10 comprises the end elements 193 and the central element 195. Web pieces 1% and 197, 198i and '199 connect the upper and lower chords.

The joint and abutment feature at the central portion of the upper chord is designated generally by the reference numeral 200 and is exactly the same, with the exception of the angularity of the chord members, as the structure illustrated in Figure 2 of the drawings in connection with the embodiment first described. The abutment plate 201 is inserted between the ends of the chord members 186 and 187.

Similarly the combined web and splice connection which serves to join the web pieces 196 and 197 and the lower chord elements 193 and is indicated generally by the reference numeral 204 and is the same as the piece shown at 50 in Figure l of the drawings with the exception that the lower chord connecting plate is somewhat wider and is provided with two rows of bolts 205.

A horizontal extension framework includes the piece 7 207 which is aligned with the substantially horizontal elements 186 and 187 of the upper chord and is supported at its outer end by means of the vertical framing 208 which extends upwardly from the heel connections of the aligned tandem trusses. A further continuation of this roof supporting framework is shown at 209. The right-hand end of the roof supporting piece 207 rests upon the bevelled right-hand end portion of the inclined upper chord element 185 as at 210 and is joined into the connection between the upper chord pieces 185 and A metal abutment plate 212 is disposed between the abutting portions of the chord elements 185 and 186 and the ends of all three of the elements 186, 187 and 207 are joined by means of the plate 215, this connection being shown to best advantage in the large view of Figure 12. The plate 215 is bolted to the end portion of the chord member 186 by means of the bolts 216, and to the end portion of the chord element 185 by means of the bolts 217 and a bolt 21S serves to connect the plate with the end of the roof supporting piece 207. An angle extension plate 220 is welded to the plate 215 and is connected to the web strut 196 as by means of the bolts 222.

The conjoined heel constructions of the adjacent truss assemblies 175 and 176 will now be described with particular reference to Figures 11 and 13. The post or column 179 is surmounted by a bearing plate 225 which may be secured against horizontal movement by means of the angle brackets 226. U-shaped straps 230 surround the bevelled-off ends of the upper chord members 185 and lower chord members 193 and these members may also be further connected by means of the bolts 232. Each of the straps 230 is provided with tight portions 235 into which are interposed the abutment plate 236. Outer cheek plates 238 are secured along the side of the arm portions of the U-shaped straps 230 as by means of the bolts which serve to secure these straps to the members 185. As clearly shown in Figures 11 and 13, the whole construction of the next truss 176 is formed in exactly the same way and the various parts have been indicated by the same reference numerals primed.

The upright 208 which extends vertically from the double heel construction may be secured to one of the bolts 232 by means of the angle piece 240 and X-braces 241 may be used to strengthen the structure. Also, any number of intermediate upright framing members such as indicated at 242 may 'be provided along the lengths of the elements 185 and 207, and any convenient bracket or saddle constructions such as shown at 245, or connecting brackets 246, may be provided in this connection.

Various changes and modifications may be made in the structures described as examples in the present specification without departing from the scope of the inveni tion as defined by the subjoined claim. For example, the metal plate connections between the chord members and the web members may be made of angle pieces instead of flat plates for additional strength; shear plates or other connecting devices may be used in conjunction with the bolts used and also single bolts may be used in the web connections inasmuch as the composite unitary steel connecting plate is firmly held by its fastenings to the upper chord. Other permissible variations within the scope of the invention include the moving of the upper chord panel upwardly from the parabolic position when required such as for tandem trusses; and the use of lower chord panel points at other than splice points where the length of lumber available dictates this.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

A truss construction comprising, in combination, a lower chord, an arched upper chord which comprises a plurality of substantially straight wooden elements secured end to end, and at least one web strut extending between and secured to the upper and lower chords, a metal abutment plate of considerably less area than the end areas of said upper chord elements but somewhat more than that area at which progressive failure of the elements due to yielding of the fibers thereof under compression would occur disposed between and in abutting bearing contact with a small lowermost portion of said adjacent end areas of adjoining elements, said lower small bearing areas being arranged to occur upon a conic section intersecting the lower end portions of the upper chord of the truss, thus facilitating designing and layingout of the truss, rendering innocuous workmens errors in angle cutting the ends of the upper chord elements, and reducing both the bending stresses and bending deflection of the upper chord elements, and at least one joint strap connecting each pair of adjacent ends of adjoining elements of said upper chord, said strap being located in generally transverse alignment with said abutment plate, the area of the ends of said elements above said plate being wholly free of contact with each other.

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